Research On Properties Of Defect States In Two-dimensional Magnonic Crystals

Artificial magnonic crystals are composed of two different magneticmaterials periodically arranged in space, which are another kind of artificialmicro-structure composite materials. The previous works show that under theappropriate conditions, the spin wave will be forbidden to propagate by theperiodic structure, and the gap will be appeared in the band structures ofmagnonic crystals. All of the potential applications are aimed to control andmanipulate localizations or propagations of spin waves in magnonic crystals,and the aritficial crystals with band gaps can be used as the fabricatingmaterials of spin-wave filter, guide, resonators and others.In this dissertation, based on the micro-cosmic mechanism of magneticinteractions, we theoretically study the dispersion relations of spin waves intwo-dimensional magnonic crystals, based on the possible applications ofmagnonic crystals in spin-wave devices, designing appropriate magnoniccrystals such as different defect structures, magnonic crystal flats and so on.The crucial parameters also were discussed to realize or to control localization,delocalization, interaction and propagation of spin waves, and expect to givesome valuable theoretical references into magnonic crystal basedexperimental investigations or practical devices in the future.Using the plane-wave expansion method under supercell approximation,band structures of spin waves propagating in two-dimensional magnoniccrystals with point defects and magnetization field distributions of somedefect modes are theoretically investigated, and band structures oftwo-dimensional magnonic crystals with different defect filling fraction arealso studied. And then, we calculate structures of spin waves propagating intwo-dimensional magnonic crystals with coupling multi-point defects and magnetization field distributions of some defect modes. The results show thatby using the coupling characteristics of defect modes make the energies ofpoint defect modes propagate along the direction of the multi-point defects inthese structures. Utilizing this properties, two-dimensional magnonic crystalscan be used as the fabricating materials of spin-wave waveguides.